Hi Robin, and welcome to the club.
Like you, I have admired the s type for some years, and although I don't do more than 7,000 miles a year I went for the 2.7 diesel, which in 3 and half years has been very reliable. It is our only car, as SWMBO parted with her Red XR3i convertible 10 years ago saying that we no longer needed 2 cars.
I don't do many long journeys, and although I was told that the DPF and the EGR valves could cause a problem, neither have ever bothered me.
The Petrol engined cars have very good engines, and are most reliable.
The s type can suffer with rust in the sills, so a check behind the plastic covers is worthwhile.
Regards,
Peter.